The present invention relates to preformed concrete slabs for construction purposes and a method of forming a floor assembly therefrom.
In the erection of large buildings having concrete floors, it is conventional to provide channels within the concrete for the passage of electrical lines used to provide power and communications to various parts of the building. Typically, a channel arrangement for the electrical lines is provided by forming hollow areas within the concrete or by embedding pipes or ducts therein. When ducts are used, interior partitions separate the duct into parallel channels. In the case where channels are metal, the channels serve to shield conductors for communication purposes positioned in selected channels from the influence of magnetic fields generated by power lines within adjacent channels. For example, if a metal ductwork is divided into three parallel channels by interior metallic partitions, the power transmission lines typically are placed in one of the channels while communication lines joined to telephones, data processing units, etc., are selectively positioned in adjacent channels. Consequently, the power lines are completely enclosed within a metal shield, thereby preventing the fields they generate from interfering with the communication links.
Obviously, using a channel arrangement such as that just described, the electrical lines are oriented in a particular direction with respect to the building under construction. If channels are provided in the several preformed slabs which are used to construct a floor of the building under construction, the result is a multiplicity of sets of parallel channels known as raceways. In order to complete a network of electrical lines, it is therefore necessary to provide further channels extending substantially transversely to the multiplicity of raceways embedded in the concrete slabs. This is accomplished by additional channel arrangements called headers. To provide a passage from a header to the raceways in the concrete slab, access units are provided at the points of overlapping intersection between the header and the raceways. An access unit typically is an open-ended device positioned to overlap knock-out holes provided in the header and the embedded raceways. Accordingly, to connect, for example, a main power line within the header to a selected power line positioned in a specific raceway, knockouts are removed at the points of overlap of the header and the appropriate raceway, and a splice is made which passes through the knock-outs. Also, to provide passages from the raceways to specific areas of the final floor surface, additional access units are selectively positioned over knock-outs in the raceways.
Conventionally, when a building is constructed using preformed slabs, each slab is positioned in its proper location extending between support beams. The access units are placed on top of the slabs at the locations prescribed by the building plans and headers are appropriately positioned. Concrete then is poured to surround the access units and headers, thereby covering the slabs and bringing the concrete floor up to its prescribed final level where its surface is finished.
From the foregoing discussion, it can be seen that while the use of preformed slabs facilitates the construction of the floor, and reduces the amount of concrete which must be poured at the construction site, nevertheless, a substantial concrete pouring is required in order to complete the encapsulation of the electrical channels and to provide a smooth surface to the floor.
In accordance with the present invention, an improved method is provided for fabricating preformed slabs and forming a floor assembly therefrom so as to eliminate the requirement that an entire floor be poured on site.